chore(.machine_readable): convert 6a2 checkpoint files from Scheme to A2ML

Convert all .machine_readable/6a2/ files from Guile Scheme format to
A2ML (a2ml) format. Preserves all data (project name, version, milestones,
blockers, actions) in the A2ML TOML-like structure.

Also fills in unfilled template placeholders ({{CURRENT_YEAR}}, {{AUTHOR}},
etc.) with concrete values.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/6a2/META.a2ml

@@ -9,7 +9,7 @@ version = "0.1.0"
 last-updated = "2026-03-02"
 
 [project-info]
-type = "{{PROJECT_TYPE}}"  # library | binary | monorepo | service | website
+type = "library"  # TODO: update type (library|binary|service|website|monorepo)  # library | binary | monorepo | service | website
 languages = []             # e.g. ["rust", "zig", "idris2"]
 license = "PMPL-1.0-or-later"
 author = "Jonathan D.A. Jewell (hyperpolymath)"